Is there a 'second Earth' 41 light years away?

A planetary system that may contain life has been found in orbit around a Sun-like star 41 light years from Earth - or 240,906,832,298,136 miles.

The discovery has excited Nasa, where astronomer Dr Geoff Marcy told a conference last night: "It has me jumping out of my socks."

The most significant point of the discovery is that it indicates that planets with temperatures similar to Earth and a plentiful supply of liquid water could be common in the universe. Scientists have guessed at this possibility for some years, but this is the first hard evidence.

Nasa announced that for the first time five planets, all of them huge, have been found in orbit around a star known as 55 Cancri.

"This planetary system is a souped-up version of our own with planets making nearly circular orbits around the parent star," said Dr Marcy.

It is the fourth planet from 55 Cancri that is causing the sensation. Although it is 45 times the mass of Earth and is probably a gas giant similar to Saturn or Neptune in composition and appearance, it is located in what astronomers call the "Goldilocks zone".

This means that it is not too hot, not too cold, but just about right for the existence of water and life.

The scientists said that although there is unlikely to be life on the actual giant planet, it probably has rocky moons in orbit around it and those moons are prime possibilities. At this stage there are no telescopes or other methods powerful enough to detect such moons but new instruments are expected within the next decade that will show definitively if the expected moons exist.

55 Cancri, in the constellation Cancer, has been under study for nearly two decades but only now has positive evidence of the planets been determined.

The innermost planet is about the size of Neptune and circles the parent star in less than three days at a distance of about 3.5million miles.

The farthest-out planet is four times as massive as Jupiter and takes 14 Earth years to orbit at a distance of about 539million miles - a little further out than our solar system's Jupiter. Planets in between are in the range of Jupiter and Saturn.

The fourth one out, about 72.5million miles from the parent star, is in an orbit similar to Venus's. But 55 Cancri is slightly fainter and less hot than our own sun, putting the star in a habitable zone that will allow water to remain liquid on a rocky surface.

If there is in fact a large rocky moon in orbit around the planet it will be slightly warmer than Earth, said Dr Jonathan Lunine, a planetary scientist at the University of Arizona. "Finding new Earths around sun-like stars is the holy grail for planethunters," he said.

Dr Marcy added: "There are likely to be billions more such systems waiting to be found. There could be 20billion planetary systems in the Milky Way alone."